Blended pigment



Patentes lane 30, ieee BLENDED PHGMENT James E.. ge, Newark, N. Si., assigner, by rnesne assients, to E. l. du Pont de Nemours and Company, a corporation ot Delaware Application. October 30, 11934, Serial No. 750,65

The present invention relates to pigments consisting of TiOz of pigment quality mechanif cally mixed with an alkaline earth metal sulfate and is particularly distinguished by the char- 5 acteristics of the components, TiOz and alkaline earth metal sulfatos. of my invention the alkaline earth metal sulfate acts as a. reinforcing pigment in contradistinction to prior art pigment mixtures in which the alkaline earth metal sulfate acts merely as an ine diluent. i'

The invention is applicable for calcium base, strontium base as well as barium base pigments, though at the present time strontium sulfate, due to its cost is not available for the commercial production and use in pigments of this type. My description of my novel pigments and methods oi making them will therefore be limited to calcium and barium base pigments. It will be understood that the expression alkaline earth metal asused herein excludes magnesium which is sometimes but loosely referred to as an alkaline earth'metal. This exclusion is quite logical inasmuch as this invention deals with substantially water insoluble sulfate extenders such as calcium, strontium, or barium sulfate, and magnesium sulfate is freely soluble in water.

It has heretofore been axiomatic in the paint and pigment arts that only such titanium di- 30 oxide-alkaline earth metal suliatepigments are of value in which the particles of titanium dloxide are precipitated on and coalesced with an alkaline earth metal sulfate, and that the valuable properties of such coalesced pigments are not reproducible by mere mechanical mixing or blending of the components.

This co-alescence of the components of the extended pigments has been produced by precipitation of one component in the presence oi and on the surface of the other component followed by cocalcination.` The expressions coalescence and coalesced as used herein are intended to indicate that the pigments have been produced by such methods.

` L. E. Barton, a pioneer in this art of coalesced pigmentg states as follows: (U. SjP. 1,155,462, Oct. 5, 1915, page l, lines 23 to 39):

The increased hiding power thus imparted to oil-paint by my novel composite titanic oxide pigments seems attributable only to my novel methods o-f producingl them which result in an extremely, ii not unprecedentedly, minute subdivision of the titanic constituent and its peculiar attachment to, or coalescence with, suspended minute particles of a sulphate base, or ex- In the blended pigments tender, usually preponderating, but which has, however, by itself in oil no hiding power; and I am satised that equally good results are unobtainable thru any mere mechanical mi'xing of the same or even greater proportions of any titanic material with similar bases. otherwise produced. I

Similarly, a whole series of patents to Barton features the same idea including Numbers 1,205,144, 1,218,161, 1,234,250, 1,236,655, 1,240,405, 1,288,473, 1,409,648. These cover the period' of 1917 to 1922.

Similarly, Buckman in U. S. P. 1,402,256, states in claim 7 As a new article the hereinbefore described uncalcined composite product, distinguished as consisting essentially oi barium sulphate particles and adhering thereto particles of a titanium complex hydrolytically precipitated thereon at temperatures substantially above 100 C'. and under pressure substantially above atmosphere.

Bushman in U. S. l). 1,410,056, makes similar statements.

A later patent to Barton and Ryan U. S. P.- 1,680.,316, features the coalescence oi the T102 and the extender.

This teaching is not conned to the patent art. For example, Mr. Noel Heaton at a meeting of the Royal Society of Art, May 3, 1922, states as follows: (Reference the Chemical Trade Journal, 1922, page 565) It was found that by precipitating the titanium together with BaSOfr a physical combination of the two was formed which had better pigmentary properties than the pure oxide.

In practice it was found preferable to form the BaSOr iirst and add it in the state of pulp to the solution and precipitate the titanium on it by the process of agitation just described, page 566.

The extraordinary point was that when the combined precipitate of titanilun oxide and barium sulphate was calcined in this way, the opacity of the composite product obtained was far above the mean of that Iof the two constituents. The theory put forth by Vilashburn to account for this was that on precipitation the titanium oxide formed a coating on the surface of the particles of BaSOi.

Similarly, Mr. H. A. Gardner in the American Paint Journal, June 23, 1930, number 24, states as follows:

The composite pigments are mada up' of titanium oxide coalesced with an inert white extender pigment. In the manufacturing process surface of the particles of the white extender. A later calcination step changes the hydrated titanium oxide to the oxide (TiOz) and at the same time causes a. cementing of the components.

My own experience has in general confirmed the fact that ordinary barium and calcium suliates as commercially available or as made by standard processes, produce, when blended with TiOz, pigments which are unsatisfactory. As a matter of fact mixtures of ordinary calcium or barium sulfate with TiOz are inferior in color, tinting strength and hiding power to corresponding amounts oi TiOz, whereas compositions in which the same amounts of T102 arecoalesced with the same amount of alkaline earth metal sulfate are equal or sli tly superior to the same amount oi straight TA z, and as far as I am aware all composite T102 alkaline earth metal sulfate pigments commercially available heretofore have been of the coalesced type.

I have found that unexpectedly 'one obtains pigments of a color, strength and/or power approaching that of or superior to those of .the corresponding amounts of straight T102 if one adjusts thepigmenting properties oi; the TiOa component and those of the alkaline earth metal sulfate component to certain values as will be described below.

The pigments obtained in this manner are, though physically different, equivalent or even superior in pigment quality to the best coalesced. pigments of the same vchemical composition in respect to TiOz and alkaline earth metal sulfate.

lt has been necessary in order to obtain the -desired alkaline earth metal sulfatos to devise new processes and treatments or to modify existing processes of making alkaline earth metal sulfates as will be explained further on.

It should be understood that the alkaline earth metal sulfatesas used in my invention should exist in the lform of individual particles not attached to, or coprecipitated with, or coalesced with any other pigmenting materials, and that my claims should be interpreted to exclude from the blends any such coprecipitated or coalesced alkaline earth metal sulfates.

For a better understanding of the characteristics of the T102 and alkaline earth metal sulfates required to produce the desired extended pigments of my invention it will be necessary to explain the various terms used herein and the methods of testing employed:

@olor Color is the apparent brightness and tint of the pigment in an oil paste as measured relative to a standard similarly prepared and is expressed in units on an arbitrary scale.

The pastes are prepared by mulling the pigment with acid refined linseed oil of `acid number 12.5 to form a thick paste. The sample to be tested and the standard are placed beside each other on a colorless microscope slide 2"x 3' in daubs about 1%x 1". The daubs should be in sharp contact without air bubbles in the contact line and should be suiciently thick to cut ofi all transmitted light. The pastos are then graded under north sky light for dierence in appearance.. The minimum perceptible difference in brightness is called one point of color. The

sample is graded in full points from the standard. Dierences in tint are important. In the 9,046,054 hydrated titanium oxide is precipitated upon the case oi white pigments a yellowish cast of the sample is penalized in .the grading to the extent of one or more points as it is barely perceptible or clearly vident. On the other hand a bluish cast relative to the standard is desirable and con- 5 sequently modiiies Vthe brightness grading upward. This procedure is essentially the one described by J. E. Booge and H. E. Eastlack in the Paint, Oil and Chemical Review, April 9, 1924.

Pigments suitable for use in high grade white 10 paints should rate 12 or higher on the arbitrary scale of the above color test.

Refiectance u Reflectance is the ratioof light reflection from the sample to be tested to light reflected from standard fumed MgO Vunder conditions of` equal and essentially diffuse illumination and as viewed from a. direction normal to the surface of the 20 sample. Values are determined and reported corresponding to noon sunlight-illumination and to the spectral region centering at 459 millimicrons, in the blue region. i

The yaluesoi reflectance as used herein were 35 measured by use of the Priest reiiectometer which ls ementially that described as the Priest- Lange reectometer in the American Enameler for August 1933, pp. 3-4.

The samples and standard are illuminated 3 dliusely and viewed at right angles to their respective surfaces. The illumination is approximately completely diffused except for the viewing hole, i om. in diameter, located about i5 cm. from the sample. The gradings are obtained by illaminating the sphere wall, from which the sample is illuminated, with gas lled incandescent lamps and viewing sample and standard through a. piece of Corning daylight glass (melt of 1925) of suitable density for the noon sun- 40 light grading, or a suitable blue illter for the blue region grading.

The brightness of each sample illuminated in this way was determined relative to that cimag- Y nesium oxide by a Martens photometer accord- 45 ing to standard procedure.

The samples were prepared for test by pressing the dry pigment into a trough, using ilne ground plate glass to form a. flat-matte surface. 5o

Hiding power Hiding power is dened as the area covered, in cm2, by one gram of pigment as contained in a 5 paste of the stated oil content when 'spread at a 5 thickness just sumcient to obliterate, visually, the

vline of demarcation between the llm as spread over a. black surface/at the finite andycritical iilm thickness and at infinite thickness. 60 The instrument used for this determination is vthe `'.vell type cryptometer. The instrument and Pastes were prepared by mulling the pigment 70V and oil for 5 minutes with a 15 1b. weighted muller. The oil used was acid rened linseed oil of 12.5 acid number for BaSOl blends; for calcium sulfate blends a mixture was used con- Sistine of 59% olfA this oil and-50% of a kettle 'I5 bodied linseed oil of 13.4 acid number and Gardner-Holdt body Z. in case of the BaSOi blends the oil portion of the pastes represented 68.5% by volume of the total. The Wide range of the oil absorption of the calcium sulfate blends made the use of equal oil contents impractical and the use of the simple acid refined linseed oil impossible. Pastes were therefore prepared with the above oil mixture to equal consistencies as judged by the spatula.

The pastes used for TiO2 were prepared in the same way and contained 68.5% by volume of acid refined oil :for comparisons with the titanic oxidebarium sulfate pigment. For comparisons with titanic oxide-calcium sulfate pigments, the pastes were made to equal consistency using the mixture of kettied bodied and acid rened linseed oils described above.

Hiding vpower is calculated from the Wedge reading of the Pfund cry-ptometer for the critical hiding thickness as follows:

in which X=wedge constant (0.000743 for Wedge used) L=wedge reading S=speciiic gravity of paste P=per cent `pigment in paste Tinting strength l Tinting strength is a measure of the effectiveness of a white pigment in covering up the tint of a colored pigmentfmixed with it. The property is relative in nature and results are obtained in comparison with another pigment used as standard. These results depend on the standard for magnitud-e but are independent of the standard foi-'relative order.

Pastes are prepared by mulling together the white pigment, ultramar-ine blue, and acid refined llnseed oil of 12.5 acid number. The proportions used were 3.0 grams of White pigment, 0.3 grams of ultramarine blue and 1.0 cc. of oil for barium sulfate blends. rI'he propor- -tions oi pigment and blue were the same for the calcium sulfate blends but due to the wide range of oil absorptions larger quantities oi oil were required for the latter. To determine'the tinting strength oie the T102 content or" the blended pigments, the same amount Vof blue andoil were' mulled with the corresponding amount oi pigment TiOz. Mulllng' was for 3 minutes with a, 15 lb. weighted mullet'.

Standards are prepared in the same manner and lower strength (that `is less or more deeplyV tinted) and not more than 5% apart in strength. The proportion of blue used in the standard fpaste to give any desired strength is inversely proportional to that strength. Thus one standard is called arbitrarily 210 which corresponds to 0.3 grams of blue in the paste. The blue requiredto give 190 strength is Oil absorption Oil absorption is the amount of oil, in grams, required to wet 100 grams of pigment.

The method of testing is described in Gardners book cited above under Hiding power, on pages 475-7.

A 5 gram sample is used. Acid reiined linseed cil of acid number 12.5 is added slowl,l from a burette and worked into the pigment with a spatula on a smooth glass plate. The addition of oil is continued a drop or two at a time until the pigment can bercollected in one coherent mass adhering to the spatula but not wetting the glass. The amountof oil used to wet the pigment is read from the burette.

Particle size Particle size as used herein refers to the frequency particle size average which may be described as the number Weighted average diameter. y

The method of measurement was essentially that described by Henry Green, Paint, Oil and Chemical Review, volume 88,#10, page 10, March 10, 1927.

Pigment dispersione were prepared in dammar gum for"ii02 and in a mixture of 56% Canada balsam, 20% ll/Iichlers ketone, and 14% asphaltum for the alkaline earth metal sulfatos and for the titanium dioxide-alkaline earth metal sulfate pigments. The preparations were photographed at 1500 diameters (except for very coarse material) using transmitted ultraviolet light of 366 millimicrons from a mercury arc.

The initial photographs were enlarged 3% times to a total magnification of 5000 diameters. Particles were classified in 1/2 mm. intervals (corresponding to 0.1 micron actual size). Each determination was based upon a count of at least 750 particles classified into the above sizeA classes measuring in each case the horizontal diameter. The frequency particle size distribution thus obtained was then converted to a frequency per cent distribution yielding the percentage of particles in each class.

Frequency particle size average is defined by the expression nidli-Hzdzi'nsda-i- --i-nmdm F' P' SA'- erlernen-+11..

Where m is the number of particles in a size class the average diameter .of which is (11,112 is the nurnber of particles in a size class the average diameter of which is d2, and so on until the largest .size class counted (nm, dm) is reached.

The optical system is incapable oi' resolving material below approximately 02p in the case of the alkaline earth metal sulfates and below a somewhat smaller (about 0.15;i) limiting size in the case of TiOz. Particles of sizes signicantly below these limiting sizesare not shown by this method, of determining particle sizes.

It would appear unnecessary for the purposes of the present invention to give consideration to particles of a neness below about 0.2/4 as the determining factor in my inventionis the absence of substantial' amounts ofparticles above certain limits.

Having explained the terms to be used herein I can now proceed with a detailed description of my invention.

This invention consists in selecting a titanium dioxide and an alkaline earth metal sulfate both ci specic particle size and other characteristics and mechanically 'mixing or blending them, whereby I obtain a blended pigment in which the individual particles of TiOs and sulfate exist independently side by side. These novel pigments are further characterized as being equivalent in pigment properties, namely hiding power and/or tinting strength, and reflectance, brightness, etc. to coalesced pigments of substantially the same chemical composition. These blends are also, within certain limits of composition, superior in pigment properties to the corresponding amounts of the T102 contained therein.

Description of the properties ci the components The TiOa needed in my invention must have a frequency particle size average ci not more than 0.5 microns and atA least 90% of said particles of said TiOz must be not greater than 1.5 microns;

rthe TiOz should also have a hiding power of t least 90 cm2/gm and preferably areectance of at least 0.94. The TiOa must also be of the type such as used for pigment purposes, i. e. it must be free from colored impurities, it should be ci crystalline nature, such as is developed by heat treatments of precipitated h'ydrous titanium oinde and to indicate the generally well lmown properties of I ously aiiect pigmenting properties.

The alkaline earth metal sulfate needed in my invention must have a* frequency particle size average of not more than 0.75 microns and at least 90% of said particles of allg-aline earth noetal sulfate must not be greater than 1.5 microns. The alkaline earth metal sulfates have such low hiding power and tinting strength that these characteristics are practicaiiy immaterial in respect to the pigment properties of the blends made therefrom. The alkaline earth metal sulfates should, however, have a reiiectance in the blue region of at least 0.94, preferably at least 0.975.

Description of the blended pigments I have round that by mechanically mixing or blending T102 and alkaline earth metal sulfates of the .above characteristics, I obtain pigments which in hiding power and tinting strength are equivalent or even superior to coalesce pigments ofthe same chemical composition.

it is of course understood that coalesccnceprocesses may produce pigments of various qualities. I, however, have madeall comparisons ci' my blended pigments with the best coalesced pig ments I know oi, namely, such products which have been madeby processes combining the dismade with such coalesoed pigments of maximum l properties. y

In tinting strength my novel pigments as well as the coalesced pigments are substantially equal or slightly superior to the corresponding amounts of straight T102 of the same characteristics.

This is illustrated' by the following table representing measurements of typical pigments.

Barium base pig- Calcium base pig- Per ment ment Cent Straight T103 Tio:

Coalesced Blended Coalcsced Blended 29. C'- 177 ec. e isa The situation respect to hiding power is somewhat diferent. I found that hiding powers of coalesced pigments run parallel to the hidingz power cf straight TiOz up to about 30 to 35% TiO-z content of the'pigments and for pigments containing more 'IiOa Athe hiding power does not increase at the same rate as that corresponding to the same amounts of TiOz.

In the case of blended pigments the vhiding power of blends made Within the limits of my invention is, in pigments containing up to from 20 to 40% TiO-i, substantially greater than that of coalesced pigments and straight T102, but it then also falls off at higher TiOz percentages.

This is particularly noticeable for barium base pigments and can be illustrated, for instance.A

as follows:

The average hiding power of a number of coalesced barium base pigments and of an average T102 content of 25.5% was found to be 25.5.

The average hiding power of a number or' blended barium `base pigments and of an average TiOz content of 25.0% was found to be 32.2.

In general -barium base blended pigments; according to my invention, have a. hiding power greater than 25 sq. cin/g. for a 20% TiOz blend, increasing by one half sq. cin/g. in hiding power for each additional one per cent increment in TiOfz content up to 35 sq. cm/g. for a 49% TiOz blend.

Color and reilectance depend to a large extent upon the purity of the components and the treatments to which they were submitted before blending. To duplicate these properties of the coalesced pigments it is necessary to employ very pure T102 and alkaline earth metal sulfates,

traces of heavy metals such for instance as iron in the alkaline earth metal sulfate greatly aiect (for instance 5Y-9.95/0.05 in the Munsell color scale). Itis therefore preferabletouse an alkaline earth metal sulfate of areectance even better than that of the T102 with which it is to be blended. An alkaline earth metal sulfate of a 'reiiectance of 0.975 will safely take care of any slight yellowish cast in the TiOs.

I have found that reflectance in the blue region is of particular importance as determining the color of my blended pigments, and particularly the color of paints containing such pigments, it being necessary that the pigments have a reflectance in the blue region greater than about 0.950 for use in the highest grade white paints.

Commercial coalesced barium and calcium base pigments have a coloifrom 13 to 15.

Colors oi this range/altare easily duplicated by bien-ding pigment 'I'iOz'with alkaline earth metal sulfates of a. reflectance above about 0.94 and of a particle size such as specii-led in my invention.

The oil absorption of a pigment is another very important property where my novel blended pigments oder decided advantages over coalesced pigments.

For certain types of paints such as gloss enamels a low oil absorption' is desired; for flat, or matte paints a high oil absorption is preferred.

It appears now that there is not much latitude in varying the oil absorption of coalesced pigments. One important factor which determines the oil absorption of pigments of this type is the temperature at which calcination is effected, at lowA temperature the oil absorption of an alkaline earth metal sulfate and T102 is relatively high, and it decreases with increasing temperature.

In the case of coalesced pigments the calcination temperature is determined by the very high temperature (around 950 C.) required by the T102 for development of its full pigment properties, and whatever oil absorption is obtained at that temperature cannot be changed greatly, except that it might be lowered by grinding as is for instance disclosed in U. S. P. No. 1,885,921 of Nov.. l, 1932. It is therefore impossible to produce coa.- lesced pigments of high oil absorption.

I can, however, produce' blended pigments oi. substantially any oil absorption as required for practical paint uses.

When high oil absorptions are desired, I can use uncalcined alkaline earth metal sulfates or calcine them to say 400 or 500 C. only and then blend them with the TiO; if low oil absorption is desired I calcine the alkaline earth metal sulfate totemperatures above 500 C., or I calcine the blended mixture of calcined TiOs and alkaline earth 'metal sulfate to the temperature at which the desired oil absorption is developed.

I found that in this procedure where a fully developed pigment TiOz is calcined with an alkaline earth metal sulfate no coalescence takes place at the temperatures necessary to develop sufficiently low oil absorption and in the absence of substantial amounts of fluxes.. I can naturally also decrease the oil absorption of my blended pigments by grinding processes.

The greatest spread of oil absorption I have observed on nished coalesced calcium base-Tio: pigments ranges from about 13.9 to about 18.6. I have produced blended calcium base pigments of oil a Arptiori` as high as 38.8 down to less than 14, a in compositions of between about 20 and 40% T102. In the case of coalesced barium base-T102 pigments the oil absorptions in the `same range of TiOz content run from 11.7 to 14.1,

whereas I have produced blended pigments in the range from 11.7 to 16.8.

There is great practical utility in an extended titanium pigment of high oil absorption which oil absorption to my knowledge cannot be approached 5 in a finished calcium base coalesced pigment.

It will be understood that when no specific treatments are given to reduce oil absorption of the alkaline earth metal sulfates or the blends, that the oil absorption of the resulting blends 1o will be substantially greater than that of a coalesced pigment of similar chemical composition. Furthermore, thevoil absorption of the blend will be substantially higher than that of a mechanical mixture of T102 with the coarse alkaline earth l5 metal sulfates heretofore available.

`oil absorption are applied, will be above 20. Simllarly the corresponding barium sulfate blends possess oil absorptions of 14.8 or higher and usually above 15.

Properties of blends geared by particle sae characteristics The blended pigments described above have 30 all been obtained from 'IiOz and alkaline earth metal sulfates of the properties which I found necessary for giving blends of satisfactory quality.

I shall in the following compare such pigments l with pigments made outside my limits and show 35 that such unsatisfactory pigments have hiding powers or strengths below those of the corresponding amounts of straight TiOz, in other words, the alkaline earth metal sulfates within the limits of my invention act as re-enforcing pig- 40 ments in blended pigments whereas the alkaline earth metal sulfates of a coarser particle size act merely as inert diluents in blended pigments or even decrease the pigmenting values of the straight TiOz.

This statement applies particularly to such pigments where the TiOa content is from about 15 to 35% within which range there is to be found the most practical and useful pigments of this type 50 Below 15% TiOa the strength and hiding power of the pigments are too low to warrant the use of a comparatively expensive pigment such as T102. Similarly above about 35% TiOz the bulking value 55 of the pigments becomes too low and the cost too high, even at the greater strength, to compete with other white pigments such as lithopone, etc.

Y If, for example, an extended pigment of higher TiOz content is used in a paint, the amount re-l 60 quired for satisfactory hiding power is not sufficient to impart the necessary body or thick consistency for good brushing and other practical application properties.

On the attached drawing Fig. 1 shows the rela- 65 tionship of hiding power vs. particle size of bariuml sulfate in barium base-TiOz blended pigments of my invention at various TiOz concentrations, the TiOz being in all instances of a frequency particle size average below 0.5 microns and at least 70 %-of said T102 particles being of a particle size not greater than 1.5 microns.

The dotted line crossing diagonally the figure represents the theoretical hiding power of the Tio: plus that of the barium sulfate, assuming 75.

the latter to be 5 for 100% barium sulfate. It was noted that the difference in particle size of the barium sulfate within the range of Vproducts which could be used for blending with TiOz to produce paints, does not measurably aiect the hiding power inherent in the barium sulfate. The hiding power of-v 100% TiOz as used herein was found to be 95.

It will be seen from this gure that pigments made from a good T102 and barium sulfate in which the frequency particle size average is greater than 0.75, namely 0.78 never reach the theoretical hiding power of the straight T102 plus that of the barium sulfate (curve A) A blend made from a good T102 and a barium sulfate in which the frequency particle size average is 0.86 and in which the particles greater than 1.5 microns constitute more than 10% of the particles of the barium sulfate, has properties far below those made from ner barium sulfate (curve B). i i

Curves I, II, and III represent pigments within the scope of myinvention.

VIt will be seen that in the compositions such as are commercially useful the hiding power of the blends exceeds the theoretical hiding power of the corresponding 'IiOn plus barium sulfate.

To further illustrate the above facts, I am giving in tabular form the various data relating to 25% and 17.1% TiOa-BaSOr blends and corresponding amounts of unblended. T102. The table also includes specic data on corresponding 'coalesced pigments.

amiante fate component upon the tinting strength of ".liOz-barlum sulfate blends, lis illustrated by the following table and Fig. 2.

It will be noted that six barium sulfate samples are used ranging in frequency particle size average from 0.25 up to 0.86 microns. Each of the six barium sulfate samples has been blended with v'11"102 in six diiferent proportions so that the blends contained respectively 10, 20, 25, 30, 40, and T102. 'I'he resulting tinting strengths of the blends are tabulated below.

From 25 to 50% T10: the coarser barium sulfate reduces the inherent strength ofthe TiOa.

From th above table one may compare the tinting strength of the same (corresponding) amount of straight T102 (given in the last line T10; BeBO Pigment Fre# Fre- 95 4 98 Reiectance Rellectance No. quency 90% of quency 90% Oil Per particle 21" lm't particle Tinting lim' ib- T cent size 3&0 size omite planicies Bum Bl strength por sum B1 smy1 average avere no a ove ue ue on microns microns microigig microns light light 1---. 25. 5 165 25. 5 0. 968 0. 965 14. 4 Coalesaed pigmen 2--.. 25. 0 0. 35 l. 5 0. 25 0.4 0. 5 0. 6 0. 989 0. 987 170 34. 5 0. 958 0. 957 18. 6 Blend. 3---- 25. 0 0. 35 1. 5 0. 32 9. 6 0. 7 0. 9 0. 991 0. 986 165 32. 8 0. 964 0. 964 l5. 3 Do. 4---- 25. 0 0. 35 1. 5 v 0. 43 1. 0 1. 1 1. 3 0. 993 0. 987 185 32. 0 0. 955 0. 953 15. 3 Do. 5---. 25. 0 .0. 35 l. 5 0. 71 1. 5 1. 9 2. 3 .0. 987 0. 982 160 29. 6 0. 960 0. 962 14. 3 Do. 8-.-. 25. 0 0. 35 1. 5 0. 78 1. 5 1. 7 2. 1 0. 989 0. 989 149 26. 1 Not iltlieet- 14. 0 Do.

m e 7..-. 25. 0 0.35 1. 5 0. 86 l. 9 2. 2 2. 7 0. 995 0. 994 147 23. 0 0. 958 I 0.950 14. 0 Do. 8.--- 24. 6 0. 5 1. 5 3. 2 5. 3 5. 6 6. 4 NDI; determined 128 Not determined 9. 0 D0. 9.-.- 25.0 0.5 l. 5 154 27.8 l .Not determined Straight TiOg. 10.-- 17. 1 114 Not determined ll. l oalesied pigv men 11.-- 17. 1 0. 5 1. 5 0. 5 1. 5 Not determined 126 27. 5 Not igeer- 11. 8 Blend rn e 12.-- 17. 1 0. 5 1. 5 l 100 21 Not determined Straight T101.

#1 and 10 in this table are coalesced pigments.

#9 and 12 are straight T10: in amounts corresponding to 25 and 17.1% as indicated.

#2, 3, 4, 5, and 11 are blended pigments made within the scope of my invention, and #6, '7, and 8 are blended pigments made outside my limits.

K #6 and 7 correspond to the curves A and B of Fig. 1 and #2, 4 and 5 correspond to curves LII.

' and 111 of said figure.

It will be noted from the above table that the 25.5% T102 coalesced pigment is inferior in hiding power to the blended pigments containing barium sulfate of approximately 0.75 microns frequency particle size average. In other words, blanc xe of particleslze below approximately 0.75 microns yields blends superior in hiding power to -the coalesced pigments as heretofore available. v

Y 'I'he eifect of the particle size of the barium iiul-iA of the table) with the tinting strengths of the y blends containing the same amount of T102. This comparison shows that barium sulfate of 0.71 microns particley size characteristics or lower produces blends with tinting strengths above those of the straight T102, whereas barium sulfate o1' particle size characteristics oi' 0.78 microns or greater produces blends of lower tinting strength than the straight T102 (except for low percentages of T102).

Selected data from the above table are plotted in Fig.2 of the drawing which gives tinting strengths of Tl0a-BaS04blends in comparison with frequency particle size averages of the barium sulfate contained in the blends and with straight T10'.` at various concentrations.

y The relationships: tinting strength, and hiding power vs. particle size characteristics ofthe 'HG2-calcium sulfate blended pigment# are illustrated in the following table.

Ti02 CaSO4 Pigment o .J- 0 .L 0 :5 :5 5 90% 95% 98% g au can ns1-1 gg h n n. ma n@ g u, g 5 -Lg-s s e :s geisge 25E t a g c q o. o c. c ,uw o 1 Q m Cn u y, E S 52522 2255 e a e s e 25E-$755 gse :es .a E Z n. La a o e tri o l V29.0 Coalescedpgment 209 46.7 v17.0 2 29.5 0.35 1.5 0.2 1.5. 223 73.4 40.2 3 20.6 0.35 1.5 0. 53 0.5 0.5 0.7 212 55.8 33.0 4 20.6 0.35 1.5 0.51 0.0 1.0 1.2 109 44.7 23.1 5 29.0 0.35 1.5 0.70 1.4 1.7 2.0 192 47.0 18.0 0 20.6 0.35 1.5 2. 05 Not determined 144 4.10 10.0 7 30.4 0.5 1.5 0.57 1.5 1.7 2.0 207 15.7 s 30.9 0.5 1.5 0.01 1.1 1.3 1.7 211 15.2 o 30.0 05 1.5 0.52 1.2 1.8 2.2 200 15.9 1o 30.5 05 1.5 0.54 1.0 1.2 1.5 215 21.7 11 30.0 0.5 1.5 0.56 1.3 2.0 2.3 ma 22.3 12 30.0 0.5 1.5 S11-sight T10, 193

In this table, #l is a coalesced pigment; and

#12 is straight Ti02. These have been included for comparison purposes.

It will Abe noted that two groups of samples are included in the above table. The rst group, #2-6 inclusive, represents a systematic series prepared on a small scale under the same con- -trolled conditions except that the particle size of the calcium sulfate was intentionally varied. The second group of samples 7-11 inclusive, represents a large scale production at approximately uniform particle size characteristics ranging .from 0.5 to 0.67 frequency particle size average for the calcium sulfate component.

Comparison of tinting strength with particle size characteristics of the vcalcium sulfate shows that the blends containing calcium sulfate of a frequency particle size average of 0.33 microns or less are substantially identical to the coalesced pigment of sample #l and that the coalesced pigment containing calcium sulfates of frequency particle size average of about 0.7 are substantially identical in tinting strength with straight T102. These conclusions apply to the rst group of samples prepared on a small scale. The large production samples of the second group are substantially equal to the coalesced pigment in tinting strength at calcium sulfate particle size characteristics of 0.52 to 0.67 microns. These samples are also superior in strength to the straight T102. The higher strength of the production samples compared with the laboratory samples is ascribed to the more complete incorporation and grinding possible on the larger scale operation.

In hiding power it will be noted that a calcium sulfate of frequency particle size average of 0.70 microns or less produces equality with the coalesced pigment as available previously (sample #4 is slightly out of line, possibly due to an experimental error).

From all experimental evidence available I conclude that with calcium sulfate of frequency particle size average not greater than 0.75 microns, blended pigments result which in tinting strength are superior to straight T102 and that such blended pigments are equal to coalesced pigments of similar chemical compositions as heretofore available. On the other hand', T102- calcium sulfate blends containing calcium sulfate of coarser particle sizes are definitely inferior in strength and hiding power to coalesced pigments as heretofore available or to straight Description of the blending of the components The blending of the components Ti02 and alkaline earth metal sulfate of selected properties can be made in any desired manner provided a most thorough distribution of the one component throughout the mass of the other component is obtained.

While this can be eected in a dry state, it is in most instances more convenient to effect a wet blending. In most processes the T102 and the alkaline earth metal sulfate are obtained in the form of an aqueous paste which before being available needs only drying and crushing to break up the lumps formed during drying. Such an aqueous paste is entirely suited for blending.

The aqueous paste of the pigment T102 and the wet paste of the alkaline earth metal sulfate are then mixed with thorough agitation and the agitation preferably continued for some hours until the individual pigment particles are completely dispersed and thoroughly blended. This blended mixture is then filtered, dried and the dried cakes disintegrated.

This can then be followed by a controlled dry grinding which reduces oil absorption. This final dry grinding does not decrease the particle size of the pigment components; the reduction in oil absorption is due -to some change in surface or adsorption characteristics of the pigment particles. 1

A specic method of blending is illustrated by the following.

A slurry of barium sulfate precipitated from barium chloride with concentrated sulfuric acid was agitated with a slurry of pigment T102. The blended slurry was then adjusted by the addition of barium hydroxide to give it a slight alkalinity corresponding to 3 cc. of 1/50th normal sulfuric acid perV grams of nished pigment. The slurry was then agitated for about 24 hours, ltered, dried and the dry press cake crushed.

A convenient method of preparing a pigment T102 of the specified characteristics is, for instance, the following.

A precipitated T102 obtained according to Reissue Patent 18,854 or Patent 1,851,487 is washed thoroughly with water to remove free sulfuric acid, iron, and other impurities not firmly ab Preparation of alkaline earth metal sulfates Special procedures must be followed for the preparation of the alkaline earth metal sulfatos to obtainlproducts suitable for blending with the pigment T102. As a matter of fact I have never found as yet a commercial calcium or barium sulfate of the particle size and other characteristics which would make them available for blending with T102 according to my invention.

I shall describe in the following a few of the processes developed for producing satisfactory barium and calcium sulfatos:

Production o] barium sulfate frombarium chloride and sulfuric aci-:i It has been. @own previously that sulfuric acid will precipitate barium chloride soi'utions to produce barium sulfate and this is old in the art of chemistry. It was. however, found that certain specific conditions mustfpe maintained in this reaction to produce a barium sulfate of pre-determined particle size characteristics, color, and oil absorption values, etc. Particle size is inuenced largely by the temperature at precipitation as well as the concentration of the precipitating solutions. Q

The reectance Vand color are also influenced by the precipitating'eonditions and particularly by the purity of the solutions employed. The oil absorption runs somewhat parallel to the particle size in being influenced by concentrations and ride was Cooled to 8c, a 66 B. sulfuric acid at i y; 25 C. was then added simultaneously with ice 20 By controlling the precipitating conditions one whereby a temperature rise to only ma C. was

fates of ifrequency7 particle size averages below allowed' The precipitated barium* Sufate was 0.75 microns.

temperatures of precipitation.

is enabled by this'rprocess to obtain barium sul- Siinilarly, the oil absorption can be varied so that a blend of 75% BaSO4 arid 25% T102 will have an oil absorption jrunning above 15. A reectance as high as 0.975 and not lowery than 0.94 can likewise easily be obtained.

This process comprises the addition of pure sulfuric acid to purified bariumchloride solutions under controlled` conditions. g

The barium chloride solution is first purified by rendering it alkaline to a pH of89, oxidizing any iron present to the ferrie condition and re-V moving the precipitate by filtration. 'The pre-- fen-ed concentration of the barium chloride solution is 50-60 grams Ba per liter. Y 'I'he preferred concentration ofthe sulfuric acid is -65" B.

For extremely ne particles size barium sulfate, such as of a frequency particle size average of around 0.2 microns. the precipitation `is conducted at a low iten'lperature, for instance near Athe freezing point as obtainable by brine cooling.

At room temperature a. very useful blanc :lxe is obtained whiclris of relatively high oil absorption, which is however often desirable. 'Frome room temperature to about C. the blanc fixe f is of a frequency particle size average of between for instance 0.4 to 0.75 microns, and the product is eminently suited for blending with T102 and Q use of the*` blends in outside paints.

At temperatures substantially aboveg65 C.

at other concentrations the precipitated' barium sulfate becomes too coarse and its; blends t sulfate of similarrparticle size characteristics will be formed if for each 10 C. change in the precipitation temperature the concentration is changed by about 20 grams per liter of barium sulfate precipitated; for higher concentrations the temperature must be lowered and the temperaturev increased for lesser concentrations.

Barium sulfates have, iorinstance, been produced as follows: i Y Y 275 liters of barium chloride solution containing 56 grams Ba'per liter was purified by adiusting the pH to 3.0 and ltering.' The purified filtrate was run Y:into a wooden tank, ttedwith a wooden agitator and a rubber steam inlet. All

i than 1.5 microns.

Y amount of TiO intended to be*V blended withthe barium sulfate can begaddedwithout detriment,

operation the condensation of the steam caused dilution to 54 grams Ba per liter. Enough 66 B.

Ysulfuricfacid at 25 C. was then added over a period of 15 minutes with constant agitation to produce a slight excess ef sulfuric acid. The tem; 5 Yperature rose te 60 C. during addition of the acid.

then treated aspreviously.

The product had a frequcncyparticle size average of about 0.2 to 0.3 micronsand at least 90% 25 of the particles Ywere of a, particie size not greater This product when blended with TiOz gave a somewhat higher oil absorption than the slightly coarser barium sulfate and also a somewhat better tinting strength.

The effect of higher temperature and concentration on particle size is illustrated as follows:

275 liters of barium chloride containing 90 grams Ba per iiter was'heated with live steam to C. where the concentration was reduced to $5 about 85 grams Ba per liter.

The precipitation was made witlr60 B. sulfuric acid at 25 C. and the temperature rose to75 C during 'the addition. l

Thef frequency particle sizeY average of tlr'ie product was above 0.75 microns and the productl produced Ti02 blends of low tinting strength. When precipitating the barium sulfate 4at low temperature to produce a" product of ve'ry low particie size characteristics, it is found that the barium Ysulfate is very diiiicult to iilterithe product tending to run through filter clot'n of even the finest weave until considerable `cakegis formed. A very satisfactory remedy for this has been found which consists merely of adding a part of the TiOz which at a. later blending stage is required, before the blanc yfixe fration step. 5 to 10% ef the Vweight of the barium sulfate is usually suflcient to obtain this improvement in filtration, but amountsof 25% Ior the total 55 as this further improvesthe lterability and assures an even distribution in the final blend.

Production of barium sulfate f ronrlmr-iurn sulfide The barium sulfatesproduced froml barium suly panied by thickening, etc.

blanc fixe necessary for use in my invention Ymust possess two diiilcultly achievable qualities-i. e., the correct particle sizeV and complete freedom from sulfur and suldeg. I have found that a new process of precipitating barium sulfate from barium sulfide solution by means of a solution of an alkali sulfate may be used. In order to obtain the correct particle size, the concentrations of the precipitants, temperatures and manner of precipitation must be controlled; in order to obtain the requisite freedom from objectionable sulfur compounds, the precipitated blanc fixe must be washed with acid solution, calcined and rewashed with acid solution. The nature of these modifications will be made clear by the following example.

A barium sulfide solution of 30 B. was carefully filtered to remove all off-colored suspended matter and heated to C. A sodium sulfate solution of the requisite purity and containing 230 grams per liter of anhydrous sodium sulfatewas heated to 35 C. The two solutions were added simultaneously toa suitable precipitating tank at such rates as always to maintain a very slight excess of soluble sulfate. Good'agitation was provided. The precipitated blanc fixe was ltered and washed with water until the sulfide content was reduced to a minimum. Due to strong adsorption of sulfide complete removal by washing is impossible. 'Ihe washed cake was then repulped in water to produce a slurry containing 33% solids. 'Io this slurry was added sufiicient sulfuric acid to give, after thorough agitation, a pH of about 2.0.

The treated precipitate was then washed with Water by settling and decantation, until the supernatant liquid had a pH of 3.0 to 4.0. The

slurry was finally adjusted to neutrality (7.0 to 8.0 pH)l by addition of dilute alkali, filtered, and the filter cake dried and calcined at about 500 C. in an oxidizing atmosphere.

'I'he calcined product was quenched in Water, and the water slurry, which contains 33% solids, was given a second acid treatment identical with that applied before the calcination. The acid Itreated product was washed by decantation until the supernatant liquor had a pI-I of 4.0 to 5.0. The slurry was nally adjusted to neutrality with dilute alkali.

The blanc xe produced according to the above description possesses a frequency particle size average below 0.75 microns with at least 90% of the particles below 1.5 microns, is especially good in color with a reflectance above 0.94, andl possesses desirable high oil absorption properties. It is also free from sulfides. When blended with pigment TiOz, the blends possess hiding powers and tinting strengths equal to or better than those of the coalesced pigments of similar chemical composition, oil absorptions higher than those of the coalesced pigments, and reectances above about 0.95.

Preparation of calcium sulfate acteristics suitable for blending with TiOz ac'v cording to my invention was operated, for instance, as follows:

Slacked lime containing 150 grams CaO per liter was gradually added to 60 B. sulfuric acid until about of the acid was neutralized. The amount of sulfuric acid used was suicient to produce 1400 lbs. of precipitated calcium sulfate.

The temperature rose rapidly during the precipitation to approximately 113 C. and gradually decreased. Thetemperature was held closely to boiling during the operation and the reaction mass was maintained at that temperature with 5 continued thorough agitation until such time as very few acicular crystals remained in the slurry as could be observed under the microscope at 400 magnification. -This slurry of anhydrite was then'ltered and washed until the filtrate showed lo a pH of at least 4. 'I'he filter cake as removed from the press was repulped in fresh water and made alkaline with a small amount ci sodium hydroxide. The anhydrite slurry so obtained was then filter pressed and ready for blending with 15 TiOz or can be calcined before such blending. The slight trace of sodium hydroxide remaining with the calcium sulfate reduces the oil absorption of the product on calcination. The same effect can be obtained, even to a greater extent, 20 if any alkali metal compound is added to the calcium sulfate before calcination.

A product of excellent color and a frequency particle size average of about 0.5 microns with at least of the particles being not greater 25 than 1.5 microns was thus obtained.

In the above example I have described a method for the production of calcium sulfate possessing the specified pigmenting properties discussed above. It will be understood that I may prefer 30 in some cases to calcine this calcium sulfate for the purpose of stabilizing it against rehydration when brought into contact with water. This calcination does not change the particle size, reflectance and other essential pigmenting char- 85 acteristics. I may, for example, calcine the calcium sulfate separately and then blend or rnechanicaily mix with the T102 component of the specified pigmenting propertles, or for the sake of simplicity and ease of large scale operations I may prefer to blend or mechanically mix the l two components prior to calcination of the calcium sulfate. In case the blend is subsequently calcined, the calcination temperature is maintained below that temperature at which there may be any tendency toward cementing together or coalescing the two components.

I cite below two examples of pre-calcination of the calcium sulfate together with the properties of the blended pigment produced from such calcined calcium sulfate.

The calcium sulfate was calcined to about 800 C. and blended with a good T102. It produced a pigment with the following characteristics:

A product precipitated as above was calcined at 700 C. and dry ground.r

A Blended with a goodTiOzit produced a blended pigment of the following characteristics:

. Percent 65 'IiOz content 30.7 Strength 213 Color a 14+ Oil absorption 25.3 70

The above examples refer to the preparation of calcium Asulfate in the form oi' insoluble anhy-l drite. This is my preferred form of calcium'sulfate due to the ease with which it can be produced within the specified `limitsof pigmenting 76 properties, namely frequency particle size average, reflectance, etc. It will be understood, however, that I do not limit myself to the insoluble anhydrite modication oi' calcium sulfate and that other forms of calcium sulfate are equallyapplicable in the preparation of blended pigments of high quality. For example, gypsum is useful if produced within the specified range of pigmenting properties and subsequently blended with the TiOz component.

In the above l'. have described and discussed pigments in which only one alkaline earth metal sulfate has been blended with the TiOz. It is of course understood, that I can add more than one alkaline earth metal sulfate to the TiOz. This permits of a still greater variation in the properties of the blends, particularly lin the oil absorption, as the oil absorption of calcium sulfate blends when no special treatments are resorted to is generally higher than that of the correspondingv barium sulfate blends. Such multi-component blends can be produced in any desired way.

It is further to be understood that my blended pigmentscan be utilized in the same way as other'a pigmented compositions, or they may be mixed with other components such as natural low grade extendersor cheap precipitated extenders for the sake of economy, or with other components to produce specic properties which may be desired. Y

This further mixing normally occurs in the pigsorted to if desired for any reason.

'It is in most instanceslpreferred to avail oneself of the advantages of the novel blended pigments of my invention by producing them in a nished dry form.

It is, however, also possible to eiect the blendingof the pigment TiOz and the dry alkaline earth metal sulfate directly in the presence of a vehicle whereby paints or other pigmented compositions may be produced' with all the characteristics of strength, oil absorption, hiding power, etc. which could be produced by blending the TiOz and the alkaline earth metal sulfate' in the dry or aqueous state and then incorporating the blend into the paint vehicle.

Another possibility which is contemplated withinthe scope of myinvention is to rst separately mix thev TiOa and the barium sulfate with parts of the paint vehicle and then mix such oil pastes A to form the ilnished blended paint.

requirements: the frequency particle size aver-' age of the TiOz is not more than 0.50 microns and the frequency particle size average of the alkaline earth metal sulfate is not more than 0.75 microns and 90% of said particles of TiOz and alkaline earth metal sulfate are not greater than 1.5 microns in size, said blend being at least substantially equal in reflectance and tinting strength to a coalesced pigment of a similar composition and said blend consisting of from -50% TiOz and the balance alkaline metal earth sulfate.

2. The pigment of claim 1 in which the alkaline earth metal sulfate is calcium sulfate and the blend having an oil absorption substantially greater than that of a coalesced pigment of a similar composition.

3. A pigment comprising a mechanical blend of pigment TiOz and an alkaline earth metal sulfate, the TiOz in said blend having a frequency particle size average of notmore than 0.50 microns, the alkaline'earth metal sulfate in said blend having a frequency particle size average of not more than 0.75 microns, and 90% of the ,particles of said TiOz and alkaline earth metal sulfatebeing not greater than 1.5 microns in size, said blend containing from to 40% TiOz and having a hiding power substantially greater than sq. cnn/gm for a 20% TiOz blend, increasing --by 1/2 sq. cm./gm in hiding power for each additional 1% increment in TIO: content up to 35 JAMES E. BOOGE. 

